2.28: Atoms

What could this hilly blue surface possibly be? Do you have any idea? The answer is row upon row of atoms of the metallic element nickel. The picture was created using a scanning tunneling microscope. No other microscope can make images of things as small as atoms. How small are atoms? You will find out in this lesson.

What Are Atoms?

Atoms
are the building blocks of matter. They are the smallest particles of an element that still have the element’s properties. Elements, in turn, are pure substances—such as nickel, hydrogen, and helium—that make up all kinds of matter. All the atoms of a given element are identical. They are also different from the atoms of all other elements. For an entertaining introduction to atoms by Bill Nye the Science Guy, watch the video at this URL:

Size of Atoms

Unlike bricks, atoms are extremely small. The radius of an atom is well under 1 nanometer, which is one-billionth of a meter. If a size that small is hard to imagine, consider this: trillions of atoms would fit inside the period at the end of this sentence. Although all atoms are very small, elements vary in the size of their atoms. The
Table
below
compares the sizes of atoms of more than 40 different elements. The elements in the table are represented by chemical symbols, such as H for hydrogen and He for helium. Of course, real atoms are much smaller than the circles representing them in the table.

Q:
Which element in the table has the biggest atoms?

A:
The element in the table with the biggest atoms is cesium (Cs).

Subatomic Particles

Although atoms are very tiny, they consist of even smaller particles. Three main types of particles that make up all atoms are:

protons, which have a positive electric charge.

electrons, which have a negative electric charge.

neutrons, which are neutral in electric charge.

The model in the
Figure
below
shows how these particles are arranged in an atom. The particular atom represented by the model is helium, but the particles of all atoms are arranged in the same way. At the center of the atom is a dense area called the nucleus, where all the protons and neutrons are clustered closely together. The electrons constantly move around the nucleus. Helium has two protons and two neutrons in its nucleus and two electrons moving around the nucleus. Atoms of other elements have different numbers of subatomic particles, but the number of protons always equals the number of electrons. This makes atoms neutral in charge because the positive and negative charges “cancel out.”